On the prediction of shear-layer flows with rans and SRS models

This study evaluates the ability of Reynolds-Averaged Navier-Stokes (RANS) and Scale-Resolving Simulations (SRS) models to predict turbulent shear-layer predominant (blunt- body) flows. The selected cases are the flows around a circular cylinder at Re = 3, 900 and 140, 000, and past a rounded square prism at Re = 100, 000 and incidence angles of 0 and 45 degrees. These cases exhibit complex features making numerical predictions a challenge, in particular, for turbulence modelling: shear-layers (free, boundary and wake), laminar-turbulent transition, low to moderate Reynolds numbers, flow separation and unsteadiness. In this pa- per, the aforementioned cases are simulated employing isotropic and anisotropic RANS, De- layed Detached-Eddy Simulation (DDES), eXtra Large-Eddy Simulation (XLES), and Partially- Averaged Navier-Stokes (PANS) equations. The outcome confirms that traditional isotropic RANS are unable to accurately predict such flows, whereas SRS models can significantly reduce modelling errors. Furthermore, the results show that anisotropic RANS models are an inter- esting engineering option owing to its compromise between accuracy and cost. Nonetheless, an improvement of the modelling accuracy by both anisotropic RANS and SRS models is inevitably coupled with an increase of the numerical demands

On the application of wall functions in ship viscous flows

This paper presents a numerical study on quantifying the effect of wall function boundary conditions on the calculation of ship viscous flows based on the RANS equations at model and full scale Reynolds numbers. Grid refinement studies are performed for four eddy-viscosity models with and without wall function boundary conditions. In the latter case, the conditions are imposed at varying distance to the wall. The predicted friction and pressure resistance coefficients are dependent on the location where the wall functions are applied. The magnitude of this influence depends on the Reynolds number and/or the turbulence model, reaching in some cases changes exceeding 10%. It is also shown that wall function boundary conditions may have a strong influence on the predicted wake field, especially at model scale Reynolds number

Generación de Mallas Estructuradas en Superficie

En este artículo se describe una técnica de generación de mallas estructuradas en superficie, que proporciona dos propiedades importantes: la utilización de un dominio paramétrico independiente de la forma en como la superficie es definida y la posibilidad de seleccionar el dominio computacional arbitrariamente sin tener que respetar las fronteras de la definición geométrica de la superficie. Estas propiedades son obtenidas con la introducción de una transformación de coordenadas adicional que relaciona las variables dependientes del proceso de generación de malla con las variables independientes de la definición geométrica. Se presentan algunos ejemplos de aplicación para problemas de hidrodinámica naval con diferentes descripciones geométricas: un ala elíptica en planta, una hélice marítima convencional y un casco de un buque. El método propuesto puede también ser utilizado con técnicas de generación de mallas más sofisticadas sin ninguna alteración